Direct Analysis of Native N-Linked Glycans by IR-MALDESI.

Glycan analysis by mass spectrometry has rapidly progressed due to the interest in understanding the role of glycans in disease and tumor progression. Glycans are complex molecules that pose analytical challenges due to their isomeric compositions, labile character, and ionization preferences. This study sought to demonstrate infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) as a novel approach for the direct analysis of N-linked glycans. The glycoprotein bovine fetuin was chosen for this analysis as its glycome is well-characterized and heavily composed of sialylated glycans. Native N-linked glycans produced by enzymatic cleavage (via PNGase F) of bovine fetuin were analyzed directly by IR-MALDESI in both positive and negative ionization mode. In this study, we detected 12 N-linked glycans in negative mode and 4 N-linked glycans in positive mode, a significant increase in the amount of underivatized glycans detected by other ionization sources. Importantly, all N-linked glycans detected contained at least one sialic acid residue, which are known to be labile. This work represents a critical first step for N-linked glycan analysis by IR-MALDESI with future efforts directed at mass spectrometry imaging.